Foreign Service

Motor,  Apr 2004  by Marinucci, Dan

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If a situation in the shop ever requires it, the Flow Bench will also perform the live resistance and inductance tests on injectors out of the engine.

Fuel Flow Tests

Next, the Flow Bench performs two different fuel flow tests, rapidly repeating each one three times per injector. Fig. 2 shows the results of the first one, the steady flow test. Here, each injector is held wide open just long enough for the fuel management unit to measure the pressure drop across it. Typically, dirt or clogging causes deviations during this test. For example, the injector inlet screen may be filthy, or one discharge hole in the end of a multihole injector may be clogged with carbon. Either way, it's time for some serious injector cleaning on or off the car.

Many of us have struggled with vehicles on which someone else installed the wrong set of injectors. The Flow Bench can flag an entire set of injectors that are passing too much or too little fuel because it always compares actual flow to a known standard. Here's how it works: A virtual reference or "standard" injector is located inside the fuel management unit. The equipment's microprocessor knows the actual grams per second of fuel the standard injector flows as well as the normal pressure drop across it.

The brain also knows how known-good injectors of a particular make and model should compare to the standard injector during a steady-flow test. Waekon/Hickok has already done that homework for you. In fact, the company includes software that lets you download all test results into your shop's PC or a workstation laptop. Among other features, this software contains a database of more than 6000 vehicles!

Fig. 3 shows the results of the pulsed flow test. As that name sug- gosts, the Flow Bench closely monitors the pressure drop across each injector while pulsing the injector open and closed. Realistically, a sluggish pintle won't affect wide-open injector fuel flow in the previous test. But it will cause deviations during the pulsed flow test. Here, a sticking pintle impedes fuel flow because it can't open as far or as quickly as a smooth-working pintle can.

Although there's no hard spec for the pulsed flow test, the results shouldn't vary more than about 10% to 15% from one injector to another. Plus, a pintle movement problem typically shows up on both the inductance and the pulsed flow tests. By the way, don't sweat the risk of flooding the engine during these flow tests. Waekon/Hickok says repeating the test sequence three times on a V8 puts less than an ounce of fuel into the engine.

Before I wrap up, I'll remind you that pictures are worth a thousand words. The Waekon/Hickok software included with the Flow Bench enables you to produce sharp, clear and professional-looking test reports for doubtful customers. It also makes it easy to document things such as injector readings before and after a cleaning service or injector replacement. There are a variety of other features in the software I just don't have space to cover here.